Hydrodesulfurization of hydrocarbon residuum with catalytic oil-slurry and fixed-bed zones

ABSTRACT

A process for hydrorefining, particularly, hydrodesulfurizing a hydrocarbon feedstock containing relatively high quantities of sulfur, asphaltenes, metals and ash by use of a slurry type of heat treater operated in advance of the hydrodesulfurization reactor. A catalyst is present in the heat treater in an oil slurry wherein the feedstock is desalted and demetallized and then transferred to the main reactor. The system is primarily a sulfur removal operation and hydrocarbon conversion is at a minimum.

United States Patent [1 1 Mayer et al.

[4 Oct. 23, 1973 1 1 HYDRODESULFURIZATION 0F HYDROCARBON RESIDUUM WITHCATALYTIC OlL-SLURRY AND FIXED-BED ZONES [76] Inventors: Francis X.Mayer, 5277 Whitehaven St., Baton Rouge, La. 70808; Karsten H. Moritz,114 Goltra, Basking Ridge, NJ. 07920 Primary ExaminerDelbert E. GantzAssistant ExaminerG. J. Crasanakis 1 Filed: 1971 Attorney-Leon Chasan etal.

[21] Appl. No.: 206,816

g [57] ABSTRACT [52] U 5 Cl 2o8/210 208m A process for hydrorefining,particularly, hydrodesul- [51] clog 23/02 furizing a hydrocarbonfeedstock containing relatively [58] Field 210 251 H high quantities ofsulfur, asphaltenes, metals and ash 208/212 by use of a slurry type ofheat treater operated in advanee of the hydrodesulfurization reactor. Acatalyst [56] Reterences Cited is present in the heat treater in an oilslurry wherein the feedstock is desalted and demetallized and thenUNITED STATES PATENTS transferred to the main reactor. The system isprimari P ily a sulfur removal operation and hydrocarbon conuwata t3,297,563 1/1967 Doumani 208/210 lemon a a mmlmum 3,536,607 10/1970Borst, Jr. 208/215 1-1 13 Claims, 4 Drawing Figures "figs-UL RECYCLE H27 H g COMP/P5550? fi/ji H2 5 RECUVERY Soups 796/ 7670/1 '32 no /r/wvSLURRY Alf/If 5 mean-1? soups Pflfifl 70R 1 \WlTl/DfiflW/IL .ll 1 mrm.ysr- 0/L SLl/RRY FHESH FEED PATENTEBIJBI 23 ms SHEET 1 BF 3 .EESQ

HYDRODESULFURIZATION OF HYDROCARBON RESIDUUM WITH CATALYTIC OlL-SLURRYAND FIXED-BED ZONES BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to the hydrorefining of petroleumfeedstocks, and more particularly to the catalytic hydrodesulfurizationof petroleum feedstocks containing contaminants which occur in the formof inorganic metal salts, caustic and the like and to eliminating theplugging of a catalytic reactor by contaminants.

2. Description Of The Prior Art In the conversion of hydrocarbon oilswith oxide catalysts and particularly activated metal oxides of the typecontaining alumina and/or silica alone or in combination with each otheror with other metal oxides such as thoria, zirconia, titania, chromia,molybdena, etc., contaminants in the hydrocarbon feedstocks which occurin the form of inorganic metal salts, e.g., halides and sulfates ofsodium, caustics such as sodium hydroxide, and the like have been foundto be objectionable for the reason that they tend to accumulate in thereactor, eventually increasing the back pressure in the reactor to thepoint where the reactor becomes plugged. It is also thought that thepresence of these materials on the catalyst tends to decrease theactivity of the catalyst and possibly its overall life, or both. In anyregard, it has been definitely established that certain forms oforgano-metallic compounds present in many hydrocarbon feeds, decomposeupon contact with the catalyst such that the metal is deposited thereonto the detriment of the catalyst.

High metals content residua in particular, as contrasted with lowerboiling hydrocarbon oils, produce a considerably greater amount of heavymetals deposition on the catalyst, thus causing increased catalystdeactivation, while extraneous solids and salts in the residua are theprimary cause of plugging problems. Thus, though the contaminants existin a number of forms, those which are known to cause catalystdeactivation are generally present as organo-metallic compounds of highmolecular weight, e.g., metallic porphyrins and other organo-metalliccomplexes of nickel and vanadium; and those which create pluggingproblems are generally present as alkali metal salts,e.g., halides andsulfates of sodium. The latter as a source of contamination, canberemoved by washing, adsorption and filtering to remove the salt fromthe oil. The decreased activity of the catalyst resulting from metalcontamination and poisoning, fortunately the least prevalent of the twoadverse reactions, however, is permanent and is overcome short term byincreasing the severity of the reaction. The detrimental effects ofeither type of contamination upon catalyst activity is to bedistinguished from the inactivating effect which is caused by theaccumulation of carbonaceous deposits on the catalyst material. Thus,catalyst activity may be temporarily decreased by the formation ofcarbonaceous deposits on the catalyst surface during the reaction, butsuch deposits are readily removed by combustion in a regenerationoperation as is generally practiced in the art. The accumulation ofmetal contaminants such as alkali metal salts on the catalyst, probablywithin the interstitial voids of the catalyst, is not permanentlydamaging to the catalyst, but these accumulations cannot be removed bysimple regeneration and consequently such type of inactivation isconsidered quite troublesome. If precautionary measures are not taken toprevent the deposition of inorganic residues on the catalyst, it hasbeen found that the back pressure in the catalytic reaction graduallyincreases during the course of the catalytic conversion process untilthe reactor becomes completely plugged after relatively short periods oftime, for example, 20 to 50 days depending on the severity of thereactor conditions, the salt content of the feed, and the feed rate.Short periods of continuous operation obviously adversely affect theeconomics of the operation.

Various methods have been proposed for dealing with the inorganic metalsalt contamination problem, including distilling the oil to separate itssalt content, or washing the oil if the salt happens to be soluble in adesalting agent. The distillation of the hydrocarbon feedstock is arelatively effective way of separating the feedstock from most of itsinorganic metal salt contaminants; however, distillation is a relativelycostly procedure and adds considerably to the processing cost. Removal'of the inorganic metal salt contaminants by washing is ordinarilylimited to use of aqueous washing agents since other agents which mightbe effective would prohibitively increase the cost of processing of thehydrocarbon feedstock. Accordingly, the washing procedure is at bestlimited to the removal of soluble compounds, but washing methods ingeneral do not remove all of such compounds from the feedstock.

An approach to the problem of reactor plugging due to the presence ofinorganic metal salts, caustics and the like is based upon the findingthat reactor plugging is substantially limited to the initial part ofthe main reaction zone. Thus, in a commercial reactor which may be,e.g., to 200 feet in length, it has been found that the plugging islimited, e.g., to the first few feet of the reaction zone. The plug,which generally consists of carbonaceous and salt deposits combined withcatalyst fines in the interstices of the catalyst bed substantiallyfills the voids between the catalyst particles in the first 0.5 to 3.0feet of the reaction zone, with the voidfraction increasing rapidlythereafter so that the original void-fraction is substantiallymaintained beyond the first 5 feet of the reaction zone. In order toavoid the prohibitive cost of shutting down the reactor to remove theplugging metal contaminants from the initial section of the reactionzone, it is feasible to establish a guard chamber through which thehydrocarbon residuum feedstock can be passed prior to entry of thefeedstock into the main reaction zone. The guard chamber, maintainedunder reaction temperature and pressure conditions, induces theformation of plugging deposits therein, thus lessening the amount ofcontamination in the reactor. Feedstock can thus be introduced into themain reaction zone without plugging the latter, even after long reactionperiods since at least a major portion of the plug-forming components ofthe hydrocarbon residuum feedstock are deposited in the guard chamber.It has been found that by providing a plurality of guard chambers, inseries and/or in parallel, a continuous stream of desalted feedstock canbe obtained by cycling the contaminated feedstock to one guard chamberuntil it becomes plugged and then diverting the contaminated feedstockto another guard chamber until it becomes plugged and then diverting thecontaminated feedstock to still another while the initial guard chambersare being unplugged. Thus, the guard chamber approach to removing suchcontaminants from residuum feedstocks prior to the introduction of thefeedstock into a main reaction zone is considered a highly effective wayof avoiding plugging and shutdown of large catalytic reactors.

In conventional petrochemical conversion, catalyst activity graduallydiminishes during the conversion cycle, inter alia, due to formation ofcarbonaceous deposits upon the catalyst and to some extent due tocatalyst poisoning. The latter results in very gradual, but permanentdamage to the catalyst, but the former is tempo rary and, though quiteacute, catalyst inactivity can be overcome by increasing the severity ofthe reaction. As the catalyst activity gradually decreases therefore,the reactor temperature must be gradually raised to compensate forcatalyst activity loss. This is accomplished by introducing feed gasesat a gradually increasing temperature level. Thus, the temperature ofthe reactor at end-of-run conditions is higher than at beginning-ofrunconditions. After a period of time, in any event, loss of catalystactivity precludes efficient catalyst use and the catalyst must beregenerated. During regeneration, coke and other carbonaceous materialswhich gradually deposit on the catalyst and diminish its activity, arethus removed by any one of various methods, e.g., oxidation and/or steamtreatment as is well known in the art. The regeneration can be performedin the same reactor, or in a reactor or zone separate from the reactor,and the regenerated catalyst then returned to the reactor, but in anyevent there must be a substantial time lapse before the reactor, in thiscase the guard chamber containing regenerated catalyst, is again put onstream. The start-up is again the relatively mild conditions, and thengradually, the severity is increased.

It follows that when hydrocarbon residuum feedstock is desalted bypassage of the feedstock through a guard chamber prior to itsintroduction to the main reaction zone, the guard chamber becomesplugged and eventually the plugging deposits must be removed. Thus, onthe one hand, each time a guard chamber becomes plugged it is necessaryto bypass it so that it can be treated to unplug it; and this iscertainly preferable to the alternative of dumping the entire reactor toclean up the catalyst. On the other hand, since the purpose of the guardchamber is to protect the reactor, an alternative of increasing the lifeof a guard chamber would appear detrimental to the former objective ofincreas-- ing the productivity, or on-time of the reactor. But,

guard chamber on-time is also important, and it is a worthwhile goal toincrease guard chamber life if this can be done without sacrifice ofreactor on-time. In other words, while it is desired to have theplugging occur in the guard chamber, if at all, it would also bedesirable to reduce guard chamber plugging to a minimum rate consistentwith substantially complete desalting of the feedstock to be introducedinto the main reactor zone.

In regard to another aspect of the background of the invention, it isnoted that petroleum crude oil generally contains relatively large anddetrimental amounts of hydrocarbons containing heteroatoms such assulfur, oxygen and nitrogen. In some cases, these heterohydrocarbonsexist in such great quantities that the heteroatom content, i.e.,non-hydrocarbon content, runs as high as about five percent by weight.The presence of such compounds is undesirable because of their adverseeffect both upon subsequent hydrocarbon refining operations as well asupon fuel performance.

Various techniques have been developed to remove theseheterohydrocarbons from hydrocarbon feedstocks. Generally, hydrorefiningprocesses such as hydrodesulfurization are employed. In thehydrodesulfurization reaction, the hydrocarbon feedstock together with ahydrogen-containing gas such as hydrogen, town gas, coke oven gas, lowtemperature distillation gas, water gas, gases obtained from refining orreforming mineral oils or other liquid fuels, final or recycle gasesfrom syntheses using hydrogen and the like is passed over or through acatalyst at a temperature ranging from about 650 F. to about 850 F.,whereby sulfur and other heteroatoms are substantially completelyremoved from the hydrocarbon stream.

Water also can be injected into the hydrorefining reactor for thepurpose of providing a control over the rate of temperature rise withinthe reactor.

SUMMARY OF THE INVENTION It has now been found that a hydrorefiningprocess, catalyst activity can be enhanced and catalyst plugging can besuppressed through the use of a slurry heat treater prior to the mainhydrorefining reactor, and through the use of water injected betweenstages of the main reactor.

In accordance with the present invention, an improved catalytichydrodesulfurization process is provided in which a sulfur-bearinghydrocarbon feed is admixed with hydrogen and brought into contact witha catalyst in a preliminary contact zone. The catalyst is maintained inthe form of an oil slurry and the temperature in the preliminary contactzone is sufficient to produce substantial deposition of inorganic metalsalts and some carbonaceous material on said catalyst.

The fluid hydrocarbon effluent is transferred from the preliminarycontact zone to a multi-stage reaction zone wherein the hydrocarboneffiuent is brought into contact with a catalyst. Hydrogen is also fedto the multi-stage reaction zone and water is injected between thestages of the multi-stage reaction zone to effect cooling of thereaction stream and to enhance catalyst activity.

The reaction products are separated in order to obtain a hydrocarbonstream exhibiting substantially reduced sulfur content.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing objects as well asfurther objects will become more apparent from the following detaileddescription of the preferred embodiments of the present invention, withreference to the appended drawings wherein:

FIG. 1 is a simplified flow diagram of a hydrodesulfurization process inaccordance with the present invention;

FIG. 2 is a simplified flow diagram of a modification of thehydrodesulfurization process of FIG. 1;

FIG. 3 is a further modification, in simplified form, of thehydrodesulfurization process of FIG. 1; and,

FIG. 4 is still further modification in simplified form, of thehydrodesulfurization process of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawing,there is shown a sulfurbearing hydrocarbon feed 10, illustrative ofwhich is a virgin gas oil, or a catalytic cycle oil, petroleum residuumor the like being passed together with a hydrogen rich treat gas stream13 to a slurry type of guard chamber or heat treater 11.

The slurry-heat treater 11 is a device of the type described inHydrocarbon Processing, September 1970, page 2 14, as a vapor/liquidsystem in which solid catalyst particles are maintained in a state ofcontinuous random motion by upflow of the liquid phase. Furtherdiscussions of a slurry-reactor can be found in the paper entitledRefinery Applications of the H-Oil Process, A. R. Johnson et a1,Presented at 33rd Midyear Meeting of the American Petroleum InstitutesDivision of Refining, May 16, 1968, Philadelphia, Pennsylvania.

Further, and more detailed descriptions of the slurryreaction system canbe found in the following publications:

R. B. Galbreath and A. R. Johnson, H-Oil Process is Proven by FirstCommercial Unit, Hydrocarbon Processing and Petroleum Refiner, 42, No.9, 121-124 (September 1963);

M. C. Chervenak, C. A. Johnson, E. S. Johanson, S. C. Schuman, M. Sze,H-Oil Process Primises to Improve Quality of Distillate Feed, Oil andGas Journal, Aug. 29, 1960; and,

M. C. Chervenak, C. A. Johnson, S. C. Schuman, Hydrogenation by theH-Oil Process, Paper presentedat 43rd National Metting AiCHE, Tulsa,Oklahoma (September 1960).

Hydrogen gas 12, is admixed with the hydrocarbon feed and fed to theheat treater 1 1. The heat treater is operated at elevated temperaturesin the range from at least 650 F. to 850 F., and preferably at evenhigher temperatures. Heat soaking or heat treating of the hydrocarbonfeed is achieved, resulting in increased activity in the mainhydrodesulfurizati on reactor 16.

Hoiding time inthe heat-treater' il, isfr om 10 minutes to approximately60 minutes. The hydrogen flow to the heat treater is sufficient to givesome hydrogena tion activity.

The temperature within the heat treater can be at higher temperaturesthan could be achieved in accordance with the prior art, becausedeposition of carbonaceous material at high temperatures is not aproblem in the slurry heat treater. The unit need not be shut down toreplace or regenerate the catalyst, but rather the flowable catalyst canbe withdrawn and added as required.

Furthermore, the temperature within the heat treater is uniform becauseof the flowing state of the catalyst.

It is desired to operate the heat treater at increased severity overwhat is possible with fixed bed reactors. Increased severity can'beachieved by increasing temperatures, increasing ratios of catalyst tooil and decreasing space velocities. Therefore, the high temperatureslurry heat treater can be operated at the desired high severity ascompared to a fixed bed guard chamber.

The catalyst may vary in both physical forms and chemical compositiondepending upon the type of process in which the feedstock is to beemployed. Silica and alumina based catalysts are widely employed for avariety of reactions. Silica based cracking catalysts includingnaturally occurring activated clays and synthetically preparedcomposites have been recognized .as useful in promoting catalytichydrocarbon reactions. Siliceous catalysts contain silica and frequentlyone or more promoting metal compounds such as one or more oxides orsulfides of a Group Vl B metal (e.g., molybdenum or tungsten), eitheralone or in admixture with a Group VIII compound, specifically an oxideor sulfide of nickel or cobalt. Active catalysts are also obtained bydepositing such Group VI B and/or Group VIII compounds on an aluminasupport or on a support comprising a combination of silica and alumina.Likewise other promoting oxides such as zirconia and magnesia may beemployed in conjunction with a support containing silica and/or alumina.The catalyst may be in the form of beads, tablets or extruded pellets invarious sizes depending upon the type of manipulative process to whichit will be exposed.

The heat treater or guard chamber may contain the same catalyst as isused in the main reaction zone or another catalyst; or it may contain aparticulate high surface area inert material such as bauxite, alphaalumina, activated carbon, silica gel, or the same catalyst support asis present in the main reactor without the reaction promoters depositedthereupon.

In the slurry treatment operation, metals from the hydrocarbon feed aredeposited on the catalyst as are extraneous solids such as salt, whichcontribute to the plugging of a reactor. The catalyst is added andwithdrawn periodically so that materials which cause plugging in aconventional fixed-bed reactor are removed prior to the main reactor 16.

The total catalyst employed in the heat treater 11, is generally lessthan about twenty percent, and most often is less than ten percent, ofthe weight of catalyst used in the main reactor, or reactors. Preferablyfrom about five percent to about eight percent of the catalyst used inthe main reactor, or reactors, is used in the heat treater. The depth ofcatalyst employed can range from about 5 to about 20 feet and preferablyabout 10 feet. The minimum depth required varies to some extentdepending on the space velocity (LHSV) of the feed passing through theguard chamber, which ranges generally between about 1 V/Hr./V and about10 V/Hr./V, and preferably between about 1 V/Hr./V and about 5 V/Hr./V.Space velocities within the guard chamber are usually maintained abovethose employed in the main reactor, which ranges from about 10 percentto about 40 percent of those employed in a guard chamber.

The superficial liquid mass velocity through a guard chamber rangesgenerally from about 500 lbs./hr./ft. to about 5,000 lbs./hr./ft. andpreferably from about 2,000 lbs./hr./ft. to about 3,000 lbs./hr./ft. ofguard chamber cross-section. 1

Generally, the contaminated catalysts of the guard chamber arediscarded. However, the removal of the inorganic metal salts which plugthe guard chamber can be effected, if desired, by any one of variousmethods depending upon the nature of the metal contaminants. One methodby which the catalyst material of the guard chamber may be cleaned ofplugging deposits, is simply by washing, but a more effective method isto first contact the contaminated material with an oxygencontaining gasstream, such as air or a dilute stream of oxygen, at a moderatelyelevated temperature. The oxygen treatment has the effect of removingcombustible carbonaceous deposits as well as converting insoluble metalsalts, especially those in the form of sulfides, to dispersible forms ofthe metal contaminant, such as sulfates. The oxidation step can then befollowed by washing the solubilized contaminants with an aqueous medium.To remove soluble nonvolatile salts such as sodium chloride deposits, orsulfates, the aqueous medium can be simply water. In the event that thematerials are less soluble than salt, it may be desirable to use aslightly alkaline washing medium. Alternatively rather than oxidizingthe removed catalyst material of the guard chamber prior to washing,other conventional methods for removing carbonaceous material such assteam gasification can be used.

The slurry heat treater is seen to provide numerous advantages overfixed bed reactors. For example, catalyst can be added and withdrawnwhile the unit is operating. In the ebullated state, the catalystbehaves very much as in a gas solid fluidized bed, and can be made toflow into and out of a reactor. Catalyst activity can thus be maintainedat a steady, desired level by controlling the rate of catalyst addition.Even when processing high metal content stocks, the process will operatecontinuously without downtime for replacement or regeneration ofcatalyst.

The reactor is maintained in the ebullated state by recycling liquidfrom the top of the reactor to the bottom thereby creating an isothermalsystem. This eliminates the need for costly and elaborate temperaturecontrol systems for the heat treater. The low pressure drop associatedwith the oil slurry-catalyst system permits the use of smaller catalystsizes than is practical in fixed bed systems. The 1/32 in. particle sizecatalyst which can be used in the slurry heat treater, is considerablymore effective than the larger particle size catalyst which must be usedin fixed bed reactors.

The effluent stream 14 from the heat treater 11, is

mixed with a hydrogen feedstream 15, and the admixture is fed downwardlythrough a multiple fixed bed reactor shown generally as 16. The severalbeds of the reactor designated representatively as 18, 20 and 22respectively are comprised ofa Group VI B and/or Group VIII metal. Thecatalysts are generally supported on an inorganic oxide base as forexample, alumina stabilized with silica. A preferred catalyst is amixture of cobalt or nickel and molybdenum supported on a silicastabilized alumina support. The catalyst can be presulfided inconventional manner either in situ or ex situ. These several catalystbeds within the reactor are separated one from the other and a quenchstream 24 of water or steam or, if desired, hydrogen alone or as recyclegas, alone or in mixture with the water, is fed into the spaces betweenthe beds and can be, if desired, directed against impingement baffles 25and 27 in said spaces to assure even distribution of the quench streamover the catalyst bed.

In the hydrodesulfurization process, a large quantity of heat isreleased as a result of the exothermic reactions which occur. If thisheat is not removed from the system, the reactor temperature can rise toa point where a significant cracking of the hydrocarbon stream andcatalyst deactivation occur. I-Ieretofore in an attempt to avoid theseproblems, cold quench gas, e.g., recycle gas, was injected between thecatalyst beds to reduce the reactor temperature. This procedure wasfound expensive since the gas must be cooled, separated from the liquid,scrubbed to remove contaminants and recompressed before being injectedinto the reactor. It is considered preferable in the present process toemploy liquid water as the cooling medium. The heat absorbed by thelatent heat of vaporization of the water supplies the necessary cooling.The resulting steam has been found to increase catalyst activity.Generally from about 5 to about percent by volume water can be employedto obtain the desired degree of heat removal. It has been found thatthis amount of water can raise catalyst activity 25 to about 50 percent.

The effluent from reactor 16 is partially cooled in cooling device 28and passed to a high temperature, high pressure separator 30 whereinhydrogen, hydrogen sulfide and light ends are removed via line 32 andthe desulfurized oil and water are removed via line 34.

The gaseous effluent from the separator 30 is fed via line 32 to ahydrogen sulfide recovery unit 48, wherein the hydrogen sulfide isremoved. The effluent from the recovery unit 48 is recycled via line 50with make-up hydrogen from line 12, to form hydrogen rich treat gaswhich is passed via line 12 to the heat treater l1, and via line 15, tothe main reactor 16.

The reactor conditions which are maintained in the main reactor 16 forefficient hydrodesulfurization generally require the reactor to be runat a pressure ranging from about 300 to about 3,000 psig. Preferably,however, the pressure is maintained within the reactor at from about 500to about a 1,000 psig. The temperature within the reactor varies fromthe start of the run to the end of the run, generally ranging from about650 F. to about 800 F. at the start of the run to about 850 F. at theend of the run. Preferably, however, the temperature within the reactorat the start of the run ranges from about 675 F. to about 710 F. risingto about 765 F. at the end of the run. Although lower or highertemperatures can be employed, it has been found that most economicaloperation dictates a temperature of around about 765 F. at the end ofthe run. The liquid hourly space velocity (Ll-ISV) of the reactantswithin the reactor ranges from about 0.1 to about 10 and preferablyranges from about 0.5 to about 2. The composition of the hydrogen richtreat gas fed to the reactor, including both recycle and makeuphydrogen, generally ranges from about 50 to about 90% by volume ofhydrogen, and preferably ranges from about 60 to about 80% hydrogen byvolume. On a volume basis, from about 5 to about 50% water can be addedto the reactor. Preferably, from about 10 to about 30% water can beadded and has been found to effectively cool and yet increase catalystactivity. Although it is considered preferable to inject liquid water,it is equally possible to inject steam directly into the system andstill obtain the benefits of increased catalyst activity.

Catalyst deactivation has heretofore been offset to an extent byperiodically increasing the reactor temperature. The addition of wateror steam has been found to offset catalyst deactivation at constanttemperature. Thus, catalyst life can be significantly extended bycombining water or steam injection with periodic increases in reactortemperature. When the temperature is increased, the steam addition canbe reduced to a lower level and then gradually increased until themaximum steam addition is reached. Then the temperature can be raisedand the cycle repeated again. In this manner, catalyst life can besignificantly extended. It is also considered preferable when usingeither water or steam to condense the resulting steam and recover thewater for cycling back to the reactor. If desired, instead of condensingthe steam for recycle to the water quench sprays of the reactor, thesteam can be condensed in a clean boiler to produce low pressure, i.e.,about 125 psig. steam.

The process may be modified, as for example, in the manner illustratedin FIG. 2.

It is therein shown that the combined feed streams 14 and 15 are passedthrough a preheat furnace 17 before being charged to the reactor 16.This permits the slurry-heat treater to be operated at a temperaturesubstantially below that of the reactor 16.

However, as shown in FIG. 3, in order to achieve an operatingtemperature in excess of 850 F. in the heat treater 11, the furnace isadvantageously employed to preheat the hydrogen feed stream 13 beforeadmixture with the hydrocarbon feed stream 10. Then, the combinedstreams are fed to the heat treater 11.

In FIG. 2, it is shown that the desulfurized oil from the separator 30is removed via line 34 and fed to a high temperature-low pressureseparator 36 and then passed to stripper 40 wherein steam is injectedfor further separation of hydrogen sulfide and wild naphtha. Thefinished desulfurized oil product is removed as a bottoms product fromthe stripper.

The gaseous effiuent from the high temperature-high pressure separator30, i.e., hydrogen, hydrogen sulfide and light ends, is fed via line. 32to a high pressure, cold separator and water disengaging drum 42 whereinthe steam is condensed and recycled via line 44 to the reactor. Aportion of the recycle quench stream can be withdrawn at line 45 andsent to a blowdown tank (not shown). Any entrained hydrocarbons can beseparated within drum 42 and passed via line 46 to the stripper 410. Thevaporous effluent from drum 42 is fed to a hydrogen sulfide recoveryunit 48 wherein the hydrogen sulfide is removed by contact with acaustic scrubbing agent such as methylethylamine. The effluent from thescrubber, chiefly hydrogen and light ends, is recycled via line 50 withmakeup hydrogen from line 12 to form the hydrogen rich treat gas whichis passed via line 13 into admixture with the fresh feed and then sentto the reactor. A sulfur free fuel gas stream is also recovered. Thus,the product from the process of the present invention are: (l)essentially 100 liquid volume percent of the feed as desulfurizedproduct, (2) a hydrogen sulfide stream of 95+% purity, (3) wild naphthacontaining less than aboutO.l weight sulfur, and (4) a sulfur free fuelgas.

As illustrated in the modification of FIG. 4, a portion of the effluentfrom the reactor 16 can be passed in heat exchange relationship in heatexchangers 41, 62 with the entering feed and effluent from theslurry-heat treater 11, thus providing a preheating of the feed to theslurry-heat treater 11, and consequently providing a temperature controlfor lowering the reaction temperature within the main reactor 16 belowthat value at which the slurry heat treater is operated.

The fresh feed in line 10, after heat exchange in heat exchanger 62, ispassed through the furnace 17 and then into the slurry heat treater 11.The feed, after passage through the slurry heat treater 11, is combinedwith a portion of recycle hydrogen, and make-up hydrogen, and fed intothe reactor 16. A portion of the product is discharged from the reactor16 via line 60 and another portion, as suggested, is passed in heatexchange relationship withthe fresh feed and with the ef fluent from theslurry heat treater 111 via heat exchangers 41,62.

The process as shown in FIG. 4 provides for a high temperature in theslurry-heat treater 11, and a low temperature in the reactor 16 sincethe feed to the slurry-heat treater is preheated fresh feed and effluentfrom the slurry heat treater is passed in heat exchange with cooledproduct from the reactor. The system of FIG. 4 thus provides foroperation of the slurry-heat treater at a temperature close to or evenhigher than the temperature in the reactor 16, whereas in the previouslydescribed systems, the reactor 16 may be maintained at a hightemperature relative to the slurry-heat treater.

It is thus seen that temperature control within the heat treater and themain reactor can be achieved in a variety of ways. The variouspossibilities include the use of a preheater furnace to heat thehydrogen and/or the hydrocarbon feed to the heater treater or to themain reactor.

The following is exemplary of the results obtained in treating afeedstock by passage of said feedstock, with hydrogen, through aslurry-heat treater prior to hydrodesulfurization of the feedstock in amain hydrodesulfurization reactor. The catalyst employed in the heattreater and main reactor consists of cobalt molybdate on alumina and itis one having a surface area of 315 meters per gram, a pore volume of 51cc per gram, and a surface area in A. diameter pores of 270 squaremeters per gram.

The conditions of operation of the guard chambers and reactor are asfollows:

Guard Hydrodesulfuri- Chamber zation Reactor E.l.T. Temp., F. 770 680Pressure, psig 1000 985 Inlet Gas, SCFB 3000 3000 Hydrogen 100 FeedRate, V/HrJV 1.4 0.35

The composition of the feedstock entering and leaving the guardchambers, and resultant product from the reactor, are given as follows:

Guard Hydrosul- Chamber furization Feed Effluent Product API 14.5 16.521.4

Sulfur, Wt. 3.92 3.64 1.22

Metals (V & Ni), ppm 99 90 62 Viscosity (SSFDIZZ) 247 56 27 D1 "F. I

IBP 451 451 334 What is claimed is:

1. An improved catalytic hydrodesulfurization process for converting ahydrocarbon residuum feed to useful products in a mainhydrodesulfurization reaction zone comprising:

introducing a sulfur-bearing high metals content hydrocarbon residuumand hydrogen into a preliminary contact zone which contains anoil-slurry of an active catalyst of a Group VI-B or VIII metal compound,deposited on an alumina support, the catalyst being contained in saidpreliminary contact zone in concentration less than 20 percent of theweight concentration of catalyst contained in said mainhydrodesulfurization zone, said contact being conducted at a temperatureranging from about 650 F. to about 850 F., at a contact time rangingfrom about 10 to about 60 minutes, and at superficial liquid massvelocity ranging from about 500 lbs./hr./ft. to about 5,000 lbs./hr./ft.of contact zone cross-section sufficient to produce substantialdeposition of inorganic salts and carbonaceous materials upon saidcatalyst but insufficient to produce significant conversion of theresiduum feed;

transferring the hydrocarbon residuum effluent from said preliminarycontact zone to the main hydrodesulfurization reaction zone whichcontains a plurality of fixed beds of a hydrodesulfurization catalystcomprising an active catalyst of a Group VI-B or VIII metal compound,deposited on an alumina support, contacting said residuum with saidcatalyst and with hydrogen to effect hydrodesulfurization, injectingwater between said beds to effect cooling of the reaction and to enhancecatalytic activity, and then separating the reaction effluent from saidhydrodesulfurization zone to obtain said useful products exhibitingsubstantially reduced sulfur content.

2. The process of claim 1 wherein said catalyst employed in saidpreliminary contact zone comprises a combination of oxides and/orsulfides of molybdenum or tungsten with oxides and/or sulfides of nickelor cobait.

3. The process of claim 1 wherein said residuum is a petroleum residuumobtained by the atmospheric distillation of oil, said residuumcontaining a relatively large amount of sulfur, asphaltenes, metals andash.

4. The process of claim 1 wherein the catalyst employed in saidpreliminary contact zone comprises a combination of oxides and/orsulfides of molybdenum or tungsten with oxides and/or sulfides of nickelor cobalt.

5. The process of claim 4 wherein the catalyst comprises 5 to 25 weightpercent of a sulfide of tungsten or molybdenum and l to l5 weightpercent of a sulfide of nickel or cobalt deposited on an aluminasupport.

6. The process of claim 5 wherein the support contains l to 6 weightpercent of silica.

7. The process of claim 1, wherein a portion of the vaporous effluentfrom the main hydrodesulfurization reaction zone is admixed with thesaid admixture of residuum and hydrogen prior to the introduction ofsaid admixture to said preliminary contact zone to form a combinedpreliminary contact zone feed, and the hydrocarbon effluent from saidmain reaction zone is passed in heat exchange with said combinedpreliminary contact zone feed thereby preheating said combined feed.

8. The process of claim 7, wherein said admixture is heated prior tobeing admixed with said vaporous effluent from the mainhydrodesulfurization reaction zone.

9. The process of claim 1 wherein the amount of catalyst maintained inthe preliminary contact zone is less than 10 percent of the weightpercent concentration of catalyst contained in the main reaction zone.

10. The process of claim 9 wherein the weight percent concentration ofcatalyst in the preliminary contact zone ranges from about 5 to about 8percent of that contained in the main reaction zone.

1 1. The process of claim 9 wherein the superficial liquid mass flowvelocity through the main reaction zone ranges from about 2,000lbs./hr./ft. to about 3,000 lbs./hr./ft. of contact zone cross-section.

12. The process of claim 9 wherein the space velocity (LHSV) of thehydrocarbon residuum feed passing through the preliminary contact zoneranges from about 1 V/I-lr./V to about 10 V/l-lr./V, and the spacevelocity (LHSV) of the hydrocarbon residua effluent through the mainreaction zone ranges from about 10 to about 40 percent of that employedin the preliminary contact zone.

13. The process of claim 9 wherein the particle size of the catalystmaintained in said preliminary contact zone is about l/32 inch particlesize diameter.

2. The process of claim 1 wherein said catalyst employed in saidpreliminary contact zone comprises a combination of oxides and/orsulfides of molybdenum or tungsten with oxides and/or sulfides of nickelor cobalt.
 3. The process of claim 1 wherein said residuum is apetroleum residuum obtained by the atmospheric distillation of oil, saidresiduum containing a relatively large amount of sulfur, asphaltenes,metals and ash.
 4. The process of claim 1 wherein the catalyst employedin said preliminary contact zone comprises a combination of oxidesand/or sulfides of molybdenum or tungsten with oxides and/or sulfides ofnickel or cobalt.
 5. The process of claim 4 wherein the catalystcomprises 5 to 25 weight percent of a sulfide of tungsten or molybdenumand 1 to 15 weight percent of a sulfide of nickel or cobalt deposited onan alumina support.
 6. The process of claim 5 wherein the supportcontains 1 to 6 weight percent of silica.
 7. The process of claim 1,wherein a portion of the vaporous effluent from the mainhydrodesulfurization reaction zone is admixed with the said admixture ofresiduum and hydrogen prior to the introduction of said admixture tosaid preliminary contact zone to form a combined preliminary contactzone feed, and the hydrocarbon effluent from said main reaction zone ispassed in heat exchange with said combined preliminary contact zone feedthereby preheating said combined feed.
 8. The process of claim 7,wherein said admixture is heated prior to being admixed with saidvaporous effluent from the main hydrodesulfurization reaction zone. 9.The process of claim 1 wherein the amount of catalyst maintained in thepreliminary contact zone is less than 10 percent of the weight percentconcentration of catalyst contained in the main reaction zone.
 10. Theprocess of claim 9 wherein the weight percent concentration of catalystin the preliminary contact zone ranges from about 5 to about 8 percentof that contained in the main reaction zone.
 11. The process of claim 9wherein the superficial liquid mass flow velocity through the mainreaction zone ranges from about 2, 000 lbs./hr./ft.2 to about 3,000lbs./hr./ft.2 of contact zone cross-section.
 12. The process of claim 9wherein the space velocity (LHSV) of the hydrocarbon residuum feedpassing through the preliminary contact zone ranges from about 1 V/Hr./Vto about 10 V/Hr./V, and the space velocity (LHSV) of the hydrocarbonresidua effluent through the main reaction zone ranges from about 10 toabout 40 percent of that employed in the preliminary contact zone. 13.The pRocess of claim 9 wherein the particle size of the catalystmaintained in said preliminary contact zone is about 1/32 inch particlesize diameter.